Table 1. Effect of heat stress on dairy cattle according to the temperature-humidity index (THI)

THI	Stress level	Comments
< 72	None	-
72–79	Mild – moderate stress	Dairy cows will adjust by seeking shade, increasing respiration rate, and dilating blood vessels. The effect on milk production will be minimal.
80–89	Moderate – severe stress	Both saliva production and respiration rate will increase. Feed intake may be depressed and water consumption will increase. There will be an increase in body temperature. Milk production and reproduction will be decreased.
90–98	Severe stress	Cows will become very uncomfortable due to high body temperature, rapid respiration (panting), and excessive saliva production. Milk production and reproduction will be markedly decreased.
> 98	Danger	Potential cow deaths can occur.